DE2035424C3 - Afocal attachment system for a fixed focal length lens - Google Patents

Description

V have an average refractive index in view of the predominantly negative curvatures of the Lenses of the afocal system for a magnification of up to two times the generation of a flat image guarantee. In the case of a lens system in which there are predominantly negative curved surfaces it is very difficult to produce a flat image. The negative curvatures lead to an undesirable one Curvature of the image. The front lens group requires strongly curved surfaces provide so that an overall collecting effect is achieved, although the lenses have the mentioned refractive indices exhibit.

It is useful to prevent individual light beams from being deflected too far before the optical corrections come into effect. For this purpose, positive and negative lenses are alternated arranged.

The front double lens would normally provide large pincushion distortion. By reversing the refractive indices of this double lens, it is possible to reduce this distortion to a minimum, so that only a negligibly small pincushion distortion remains. The lens III leads to a considerable pillow-shaped distortion, which is primarily due to the fifth surface R ₅ , ie the rear surface of this lens. However, the following lens IV causes a considerable barrel-shaped distortion, so that the two lenses III and IV compensate each other and the lens system is almost free of distortion.

It has been found necessary to provide a wide central air gap S _{2 in} order to separate the positive lens group from the negative lens group.

The lens IV essentially serves to correct the astigmatism of the lens system. the Lens III helps to correct the coma to a significant extent. The general form, i.e. H. the curvature of the lenses is used to keep the spherical aberration within limits.

If the magnification of the afocal attachment system is reduced to 1.8, the optical aberrations can be corrected more easily. It is possible to further reduce the dimensions of the system, which already takes up little space, to a very considerable extent if a slight decrease in magnification is allowed. Even if you reduce the angle of view, e.g. B. to 30 ^c , the aberrations can be corrected more easily. Magnification, a large angle of view and the focal ratio are the factors that create the greatest difficulties in designing a lens.

The rear negative lens group magnifies any aberration that occurs in the front positive group and also contributes its own aberration to the result. Therefore the front group must very good within the entire image field with regard to chromatic and spherical aberrations and the like be corrected.

According to the invention, the surface R ₂ in the positive lens group is made aspherical. However, one could also make the surface R ₁ or R ₃ aspherical. The choice of the area R ₂ is based, for. T. on the fact that manufacturing advantages can be achieved in this case. The area R ₂ is a cemented area. Therefore, one can create the nichispherical surface by 1-oling the lens 1 or the lens 11. The lenses can then be connected with the aid of a cement whose refractive index corresponds to that of the lens on which the aspherical surface is formed. In this case, you only need to properly sand one surface. Since the surface R _{2 is} a cemented surface, larger tolerances can be provided for the polishing of the aspherical surface.

K) see the z. B. 6 times the usual tolerances correspond.

When the rays are refracted near the outer parts of a strong double lens, such as is shown e.g. B. through the lenses! and !! is formed. prismatic scattering of rays occurs, so that it is difficult to recombine these rays into white light afterwards in the lens system. While such reunification can be achieved locally, it is difficult to achieve within a large field of view. The aspherical surface provided at R ₂ helps to prevent strong refractions on the outer parts of the double lens. This is due to the fact that the aspherical surface is less strongly curved in the areas mentioned than an ordinary spherical surface.

The formula for the aspherical surface that is used in the telescopic attachment system according to the invention is given below. It describes a surface of revolution with a height t above a flat reference surface at a distance y from the axis of rotation. This axis of rotation coincides with the optical axis. The curvature of the surface at its apex is denoted by c. It is equal to the reciprocal value of the vertex radius. The aspherical curvature becomes

j5 is determined by the coefficients jl and γ . Their values are based on the effect that the aspherical surface is supposed to exert on the light rays that do not run along the axis.

'-, TiT-V? '" ^re -

In the following, the two little space-consuming afocal telescopic attachment systems according to dei Invention described, which is optimal for use in connection with a particular camera lens are trained. Both of the objectives described below work at around twice the magnification. The position of the aperture in the camera lens for which the two lenses are optimally designed and which is arranged behind the telescopic attachment. is in Fig. 1 and 3 indicated by dash-dotted lines.

Although the two lenses provide two times the magnification, it would not be absolutely necessary to that they are designed for such a relatively high magnification. An important feature the invention consists in the space-saving structure.

Compared to the focal length of the camera lens, for Since the two lenses are optimally designed, they take up considerably less space than the up to now known telephoto lenses. If you telephoto lenses according to the invention with less than two times Produces enlargement, the dimensions can be further reduced to a considerable extent. A lens similar to the telephoto lens according to the invention, which is optimal for the same camera lens

is designed and provides only 1.8x magnification, would only take up a quarter of the space, which the objectives described here take for a 2x magnification.

The value of the refractive index η and the Abbe number V are given below for light with a wavelength of 587.6 nm. The radii of curvature and thickness values are related to the unit of length.

Lens I.

This lens is optimally corrected in order to save space in connection with the aforementioned built-up camera lens to be used, where the reciprocal value of the distance of the subject based on the unit of length is 0.1182. This lens is shown in FIG. 1 shown.

lens n. V ₁ Radii thickness and distances 0.0053 I.
II 1.58913
1.68273 61.27
44.50 R ₁ = 0.4563
R, - -0.5814
R ₁ = 0.7861 Ί =
h = 0.1692
0.0205
S ₁ = 0.2309 II 1.49782 66.95 R ₄ = 0.4530
R ₅ = 1.7911 h = 0.0634
S ₂ = 0.0730 IV 1.74400 44.77 R ₆ = 1.7624
R ₇ = 0.2473 k = 0.0148
Sj = V
Vl 1.60342
1.74400 38.03
44.77 R ₈ = 0.2513
R ₉ = -0.2166
D η f.ai-1 '5 =
k = 0.0423
0.0106

The number given for the radius of the surface R ₂ for the constants in the above formula designates the apex radius of this surface. In the present case, they have β = 2.449030 and area R ₂ is aspherical and corresponding to the previous γ = -0.784120. given formula. The values

lens

This lens is for use in conjunction with the unit of length manufacture. This ob-

with the mentioned camera lens, an afocal telescopic attachment is optimally designed in FIG. 3

forms to take photographic recordings at a depicted,

reciprocal value of the object distance of 0.0591 be r>

Lens n _i

1
II

IH
IV

V
VI

V ₁

Radii

Thickness and offsets

1.58913
1.68273

61.27
44.50

1.49782 66.95

1.74400 44.77

1.60342
1.74400

38.03
44.77

R ₁ = 0.4540 R ₂ = -0.5531 R ₃ = 0.6819

R ₄ = 0.7533, R ₅ = 3.633

R ₆ = 1.1744
R ₇ = 0.1976
R ₁₁ = 0.1982

= 0.1713
= 0.0184

f., = 0.0634

= 0.0148 S ₁ = 0.0053

0.3594

8th
S, = 0.0117

f ₅ = 0.0444

_11th

R ₉ = -0.1865 r ₆ = 0.0085
R ₁₀ = 1.0820 S ₄ = 0.0560

The values of the constants in the above formula for the aspherical surface are: // = 2.569212 and γ = - 1.017325.

Since the space-saving afocal attachment lenses according to the invention with a strong inner Working magnification and designed asymmetrically, would in practice be a change in Allow optimization by making certain changes to the types of glass. Each of the two telescopic attachment systems can be modified in this way to adapt it to a specific purpose. For certain tasks arise therefore certain optimization possibilities. The optimization area does not need to be externally in to affect to a very great extent.

1 sheet of drawings

Claims (1)

Patent claims: 1. Afocal pre-salt system door a fixed focal length lens consisting of a front one positive lens group with a first biconvex Lens, a second negative lens cemented with it and a third lens, which is on the object side convex positive meniscus is formed and from a rear, negative lens group with a negative meniscus lens convex on the object side and two lenses cemented to one another, from one of which is a biconvex lens and the other a negative lens, characterized in that that the system designed as a telescopic attachment system according to the table below is designed, based on a unit length: Lenses. Radii Thicknesses and Spacing I.
II 1.58913
1.68273 61.27
44.50 III 1.49782 66.95 IV 1.74400 44.77 V
VI 1.60342
1.74400 38.03
44.77 R ₁ = 0.4563 t, = 0.1692
R ₂ = -0.5814 i ₂ = 0.0205
R ₃ = 0.7861 S ₁ = 0.0053 R ₄ = 0.4530 I ₃ = 0.0634 R ₅ = 1.7911 S ₂ = 0.2309 R ₆ = 1.7624 / ₄ = 0.0148 R ₇ = 0.2473 S ₃ = 0.0730 R ₈ = 0.2513 J ₅ = 0.0423
R ₉ = -0.2166 I ₆ = 0.0106
R ₁₀ = 0.6912 S ₄ = 0.0687 the lenses being denoted by the Roman numerals I through VI from front to back; n _{d is} the index of refraction for a wavelength of 587.6 nm; Vi represents the Abbe number; R, and R ₃ to R] ₀ denote the radii of curvature of the lens surfaces from front to back; R _{2 is} the apex radius of an aspherical surface according to the formula '= -H - = - f + 2.449030 o ⁴ -0.784120 «/' -c ² t> and <is the distance of the points dtr aspherical surface from a flat reference surface c, where ρ is the radial zone distance from the optical axis and c is the reciprocal of R ₂ and where (is the thickness of the lenses and s is the air distance based on the unit length. 2. Afocal attachment system for a fixed focal length lens, consisting of a front one positive lens group with a first biconvex lens, a second negative cemented with it Lens and a third lens, which is designed as a positive meniscus that is convex on the object side and from a rear negative lens group with a negative meniscus lens convex on the object side and two lenses cemented together, one of which is a biconvex lens and the other the other is a negative lens, characterized in that it is designed as a telescopic attachment system System is designed according to the table below, based on a Unit length: lens I.
II III
IV V
VI V ₁ Radii Thicknesses and Spacing 1.58913
1.68273 1.60342
1.74400 61.27
44.50 1.49782 66.95 1.74400 44.77 38.03
44.77 R _x = 0.4540 f, = 0.1713 R ₂ = -0.5531 J ₂ = 0.0184
R ₃ = 0.6819 S ₁ = 0.0053 R ₄ = 0.7533 J ₃ = 0.0634 R ₃ = 3.633 S ₂ = 0.3594 R ₆ = 1.1744 t ₄ = 0.0148 R ₇ = 0.1976, S ₃ = 0.0117 R ₈ = 0.1982 t ₃ = 0.0444 Λ, = -0.1865 f ,, = 0.0085
R _1n = 1.0820 S ₄ = 0.0560 the lenses being denoted by the Roman numerals I through VI from front to back; n _ä denotes the refractive index for a wavelength of 587.6 nm; V _{d represents} the Abbe number; R, and R ₃ (, 5 to R ₁₀ denote the radii of curvature of the lens surfaces from front to back; R _{2 is} the apex radius of an aspherical surface according to the formula -— +2.569212 " ⁴ - 1.017325" / ' and r is the distance between the points of the aspherical surface and a flat reference surface. where ρ is the radial zone distance from the optical axis and c is the reciprocal of R ₂ and where t is the thickness of the lenses and s is the air distance based on the unit length> ind. The invention relates to an afocal attachment system of the type specified in the preamble of claims 1 and 2, respectively. Such a lens system is known from "Feingerätetechnik, 7th year (1958), pages 513 to 515". This known attachment system is used in conjunction with a special lens with a fixed focal length as a projection lens with a variable focal length. The special lens positioned after the iris diaphragm maintains its position in relation to the image plane at every magnification ratio, while two movable members of the afocal attachment system change their position to one another and to the rigid members in order to ensure a setting between the longest and shortest focal length. In contrast to the known projection attachment system, the invention is based on the object to create an afocal tele-attachment system which in itself is already well corrected to connect to achieve a satisfactory imaging performance with various downstream photographic lenses. This task is accomplished by training the afocal Tele attachment system with the design data according to the characterizing part of claim 1 or solved according to the data table listed in the characterizing part of claim 2. The afocal part attachment designed according to the invention enables up to two times the magnification with a compact and lightweight construction, without the chromatic and monochromatic correction of the associated camera lens affect. All lenses of the telescopic attachment are fixed relative to one another and are used for distance adjustment the lens setting of the camera lens can be used. The telescopic attachment systems according to the invention can be used particularly advantageously in connection with camera lenses which have a relatively large angle of view of up to 50 '. In particular, they are suitable to be used in conjunction with lenses where the relative opening is between I: 16 and I: 6. You can according to the The focal length of the lens with which they are to work can be scaled back. The subject matter of the invention is explained in more detail below with reference to the drawing: FIG. I shows a first embodiment of one according to FIG Invention trained afocal telescopic attachment system, F i g. Figure 2 is a graph showing the differences in the indices of refraction between adjacent lenses of the telescopic attachment according to Fig. 1, F i g. 3 shows a longitudinal section of a second afocal telescopic attachment designed according to the invention. F i g. Figure 1 shows an afocal tele-attachment system with a front positive lens group covering the lenses 1,11 and III as well as a negative rear Lens group comprising lenses IV, V and VI. These two groups are by an air gap separated, the width of which is at least 25% of the total length of the system. Both at the positive lens group as well as the negative lens group become double lenses I and II and V, respectively and VI used If a well-corrected, space-consuming header system with a to To be created to double magnification is the use of an aspherical surface one of the lenses I and II is expedient. There are particular advantages if you use the spherical Area at the cemented interface between the ίο provides lenses I and II. There are significant differences in refractive index between adjacent lenses. The refractive indices of neighboring lenses alternate between high and medium values. These significant differences are shown graphically in FIG. In the tables, the radii of curvature of the surfaces of the lenses are _{denoted by R 1} , R ₂ , etc., progressing from left to right. The thickness of the lenses and the width of the air gaps are also designated progressively from left to right with t _t , t ₂ etc. or S ₁ , S ₂ etc., respectively. The specified refractive indices apply to a wavelength of 587.6 nm and are denoted by η _Λ , while the Abbe numbers are denoted by V. For the sake of simplicity, the data tables are based on the unit of length. Here it is possible to create optimal embodiments of the invention for use in connection with certain camera lenses. In these cases it is best to use the unit length of the telescopic attachment jo systems equals the focal length of the camera lens close. If the ratio between the unit of length and the focal length is significantly less than I, the corners of the image become very vignetted and the aberrations can no longer be controlled. J5 If the header system together with a Camera lens should be used, which, in contrast to the information given above, has a has a significantly smaller angle of view, the dimensions of the attachment system can be reduced. In other words, the said ratio can be considerably smaller than 1 in this case. The afocal telescopic attachment systems according to the invention are characterized by a strong change in the refractive indices of neighboring lenses. This strong change in the refractive index primarily serves to keep the image field level. If these large differences in refractive index weren't there, the posterior one would be negative Lens group must be made considerably stronger, and this lens group would be the Predominantly affect correction of image curvature. A primary correction of the chromatic aberrations is made in the tele-attachment system by the causes both double lenses of the positive and the negative lens group. The chromatic color correction of the afocal tele-attachment with regard to lateral and longitudinal errors is effected by choosing the Abbe number. The negative lenses II, IV and VI have similar Abbe numbers with a mean value which, in the examples given here, has the value V = 45. In the case of the positive lenses 1 and HI of the front lens group, the Abbe number values are relatively high. The convex lens V of the posterior negative Lens group has a relatively low Abbe number. The concave lenses II, IV and VI have one high refractive index, while the concave lenses I, III,